Conventionally, there is known a hole plug comprising a plug main body including a head portion, a leg portion, and a flange portion; and a meltable member (see lines 8-30 of right column on page 2 and FIGS. 1 to 4 of Patent Document 1).
The aforementioned conventional hole plug is inserted into an opening portion provided in a panel to be attached, and then, a vicinity of the opening portion is heated, so that the meltable member melts, and is filled up between the flange portion and the opening portion to seal between both portions (see from line 31 to the bottom line of right column on page 2 and FIGS. 5 and 6 of the Patent Document 1).